Steps to the Reionization Epoch

A global spectral feature from the reionization epoch may be present over the whole sky. If reionization took place at 5 < zion < 20, a step should be present in the radio spectrum of the sky at 70 < < 240 MHz due to redshifted HI 21-cm line emission. The expected amplitude is well above fundamental detection limits, and the sharpness of the feature may make it distinguishable from variations due to galactic and extragalactic foregrounds. Because this is essentially a continuum measurement of a signal which occurs over the whole sky, relatively small telescopes may suffice for detection. Experiments can begin now, with a development program leading up to SKA. The measurement of fluctuations and features would be the next step – difficult, but possible with SKA.